I have doubt that cannot we use point_coord in a Fragment Shader where we are drawing a Quad.
If it is only used with point can we use Texture with point in Fragment shader
That's correct. As the documentation says, a parameter attributed with point_coord contains "two-dimensional coordinates, which range from 0.0 to 1.0 across a point primitive, specifying the location of the current fragment within the point primitive."
If you need similar parameters inside a quad, the easiest way is to include a pair of coordinates in the struct you return from your vertex function, which will then be interpolated in a perspective-correct manner across the surface of your quad.
You can either generate these coordinates based on the vertex ID in your vertex function, or generate them in advance in your host code and pass them in in a vertex buffer.
Related
I want to implement a collision detector between a moving and a static object. The way I am thinking of doing so is by checking in vertex shader every time if any vertex of the moving object intersects with the position of the static object.
By doing the above, I would get the point of collision in the vertex shader, but I want to use the variable for rendering purposes in the js file.
Is there a way to do it.
In WebGL 1 you can not directly read any data from a vertex shader. The best you can do is use the vertex shader to affect the pixels rendered in the fragment shader. So you could for example set gl_Position so nothing is rendered if it fails your test and a single pixel is rendered if the test passes. Or you can set some varying that sets certain colors based on your test results. Then you can either read the pixel with gl.readPixels or you can just pass the texture you wrote to to another shader in a different draw calls.
In WebGL2 you can use transform feedback to allow a vertex shader to write its varyings to a buffer. You can then use that buffer in other draw calls or read it's contents with gl.getSubBuffer
In WebGL2 you can also do occlusion queries which means you can try to draw something and test if it was actually drawn or if the depth buffer prevented it from being drawn.
I'm using a metal shader to draw many particles onto the screen. Each particle has its own position (which can change) and often two particles have the same position. How can I check if the texture2d I write into does not have a pixel at a certain position yet? (I want to make sure that I only draw a particle at a certain position if there hasn't been drawn a particle yet, because I get an ugly flickering if many particles are drawn at the same positon)
I've tried outTexture.read(particlePosition), but this obviously doesn't work, because of the texture access qualifier, which is access::write.
Is there a way I can have read and write access to a texture2d at the same time? (If there isn't, how could I still solve my problem?)
There are several approaches that could work here. In concurrent systems programming, what you're talking about is termed first-write wins.
1) If the particles only need to preclude other particles from being drawn (and aren't potentially obscured by other elements in the scene in the same render pass), you can write a special value to the depth buffer to signify that a fragment has already been written to a particular coordinate. For example, you'd turn on depth test (using the depth compare function Equal), clear the depth buffer to some distant value (like 1.0), and then write a value of 0.0 to the depth buffer in the fragment function. Any subsequent write to a given pixel will fail to pass the depth test and will not be drawn.
2) Use framebuffer read-back. On iOS, Metal allows you to read from the currently-bound primary renderbuffer by attributing a parameter to your fragment function with [[color(0)]]. This parameter will contain the current color value in the renderbuffer, which you can test against to determine whether it has been written to. This does require you to clear the texture to a predetermined color that will never otherwise be produced by your fragment function, so it is more limited than the above approach, and possibly less performant.
All of the above applies whether you're rendering to a drawable's texture for direct presentation to the screen, or to some offscreen texture.
To answer the read and write part : you can specify a read/write access for the output texture as such :
texture2d<float, access::read_write> outTexture [[texture(1)]],
Also, your texture descriptor must specify usage :
textureDescriptor?.usage = [.shaderRead, .shaderWrite]
I am attempting to write a fragment shader for the app that I am working on. I pass my uniform into the shader which works but it works on the entire object. I want to be able to modify the object pixel by pixel. So my code now is....
let shader = SKShader( fileNamed: "Shader.fsh" );
shader.addUniform( SKUniform( name: "value", float: 1.0 ) );
m_image.shader = shader;
Here the uniform "value" will be the same for all pixels. But, for example, let's say I want to change "value" to "0.0" after a certain amount of pixels are drawn. So for example....
shader.addUniform( SKUniform( name: "value", float: 1.0 ) );
// 100 pixels are drawn
shader.addUniform( SKUniform( name: "value", float: 0.0 ) );
Is this even possible with SKShader? Would this have to be done in the shader source?
One idea I was thinking of was using an array uniform but it doesn't appear that SKShader allows this.
Thanks for any help is advance.
In general, the word uniform means unchanging — something that's the same in all cases or situations. Such is the way of shader uniforms: even though the shader code runs independently (and in parallel) for each pixel in a rendered, images, the value of a uniform variable input to the shader is the same across all pixels.
While you could, in theory, pass an array of values into the shader representing the colors for every pixel, that's essentially the same as passing an image (or just setting a texture image on the sprite)... at that point you're using a shader for nothing.
Instead, you typically want your GLSL(ish*) code to, if it's doing anything based on pixel location, find out the pixel coordinates it's writing to and calculate a result based on that. In a shader for SKShader, you get pixel coordinates from the vec2 v_tex_coord shader variable.
(This looks like a decent tutorial (with links to others) for getting started on SpriteKit shaders. If you follow other tutorials or shader code libraries for help doing cool stuff with pixel shaders, you'll find ideas and algorithms you can reuse, but the ways they find the current output pixel will be different. In a shader for SpriteKit, you can usually safely replace gl_FragCoord with v_tex_coord.)
* SKShader doesn't use actual GLSL per se, It actually uses a subset of GLSL that automatically translates to appropriate GPU code for the device/renderer in use.
I wrote two simple WebGL demos which use a 512x512 image as texture. But the result is not what I want. I know the solution is to use projective texture mapping(or any other solutions?) but I have no idea how to implement it in my simple demos. Anyone can help?
The results are as follows(both of them are incorrect):
Codes of demos are here: https://github.com/jiazheng/WebGL-Learning/tree/master/texture
note: Both the model and texture could not be modified in my case.
In order to get perspective-correct texture mapping, you must actually be using perspective. That is, instead of narrowing the top of your polygon along the x axis, move it backwards along the z axis, and apply a standard perspective projection matrix.
I'm a little hazy on the details myself, but my understanding is that the way the perspective matrix maps the z coordinate into the w coordinate is the key to getting the GPU to interpolate along the surface “correctly”.
If you have already-perspective-warped 2D geometry, then you will have to implement some method of restoring it to 3D data, computing appropriate z values. There is no way in WebGL to get a perspective quadrilateral, because the primitives are triangles and there is not enough information in three points to define the texture mapping you're looking for unambiguously — your code must use the four points to work out the corresponding depths. Unfortunately, I don't have enough grasp of the math to advise you on the details.
You must specify vec4 texture coordinates not vec2. The 4th field in each vec4 will be homogeneous w that when divided into x and y produce your desired coordinate. This in turn should allow the perspective correction division in hardware to give you a non affine mapping within the triangle provided your numbers are correct. Now, if you use a projection matrix to transform a vec4 with w=1 in your vertex shader you should get the correct vec4 numbers ready for perspective correction going into setup and rasterization for your fragment shader. If this is unclear then you need to seek out tutorials on projective texture transformation and homogeneous coordinates in projection.
How do you implement per instance textures, vertex shaders, and pixel shaders, in the same Vertex Buffer and/or DeviceContext?
I am just trying to find the most efficient way to have different pixel shaders used by the same type of mesh, but colored differently. For example, I would like square and triangle models in the vertex buffer, and for the vertex/pixel/etc shaders to act differently based on instance data.... (If the instance data includes "dead" somehow, the shaders used to draw opaque shapes with solid colors rather than gradients are used.
Given:
1. Different model templates in Vertex Buffer, Square & Triangl, (more eventually).
Instance Buffer with [n] instances of type Square and/or Triangle, etc.
Guesses:
Things I am trying to Research to do this:
A: Can I add a Texture, VertexShader or PixelShader ID to the buffer data so that HLSL or the InputAssembly can determine which Shader to use at draw time?
B. Can I "Set" multiple Pixel and Vertex Shaders into the DeviceContext, and how do I tell DirectX to "switch" the Vertex Shader that is loaded at render time?
C. How many Shaders of each type, (Vertex, Pixel, Hull, etc), can I associate with model definitions/meshes in the default Vertex Buffer?
D. Can I use some sort of Shader Selector in HLSL?
Related C++ Code
When I create an input layout, can I do this without specifying an actual Vertex Shader, or somehow specify more than one?
NS::ThrowIfFailed(
result = NS::DeviceManager::Device->CreateInputLayout(
NS::ModelRenderer::InitialElementDescription,
2,
vertexShaderFile->Data,
vertexShaderFile->Length,
& NS::ModelRenderer::StaticInputLayout
)
);
When I set the VertexShader and PixelShader, how do I associate them with a particular model in my VertexBuffer? Is it possible to set more than one of each?
DeviceManager::DeviceContext->IASetInputLayout(ModelRenderer::StaticInputLayout.Get());
DeviceManager::DeviceContext->VSSetShader(ModelRenderer::StaticVertexShader.Get(), nullptr, 0);
DeviceManager::DeviceContext->PSSetShader(ModelRenderer::StaticPixelShader.Get(), nullptr, 0);
How do I add a Texture, VertexShader or PixelShader ID to the buffer
data so that HLSL or the InputAssembly can determine which Shader to
use at draw time?
You can't assign a Pixel Shader ID to a buffer, that's not how the pipeline works.
A / You can bind only one Vertex/Pixel Shader in a Device context at a time, which defines your pipeline, draw your geometry using this shader, then switch to another Vertex/Pixel shader as needed, draw next geometry...
B/ you can use different shaders using the same model, but that's done on cpu using VSSetShader, PSSetShader....
C/No, for same reason as in B (shaders are set on the CPU)
When I create an input layout, can I do this without specifying an actual Vertex Shader, or somehow specify more than one?
if you don't specify a vertex shader, the pipeline will consider that you draw "null" geometry, which is actually possible (and very fun), but bit out of context, if you provide geometry you need to send the vertex shader data so the runtime can match your geometry layout to the vertex input layout. You can of course create several input layouts by calling the function several times (once per vertex shader/geometry in worst case, but if two models/vertex shaders have the same layout you can omit it).
When I set the VertexShader and PixelShader, how do I associate them with a particular model in my VertexBuffer? Is it possible to set more than one of each?
You bind everything you need (Vertex/Pixel shaders, Vertex/IndexBuffer,Input layout) and call draw (or drawinstanced).